Physical layer frame format for wlan

ABSTRACT

In a method for generating a data unit for transmission via a communication channel, wherein the data unit conforms to a first communication protocol, a preamble of the data unit is generated. The preamble includes a first field having information that indicates a duration of the data unit, the first field being formatted such that the first field is decodable by a receiver device that conforms to a second communication protocol but does not conform to the first communication protocol to determine the duration of the data unit based on the first field. Additionally, the preamble is formatted such that a portion of the preamble is decodable by a receiver device that conforms to a third communication protocol but does not conform to the first communication protocol. Also, the preamble is formatted such that a receiver device that conforms to the first communication protocol can determine that the data unit conforms to the first communication protocol. A data portion of the data unit that conforms to the first communication protocol and does not conform to either (i) the second communication protocol or (ii) the third communication protocol is generated.

CROSS-REFERENCES TO RELATED APPLICATIONS

This disclosure claims the benefit of the following U.S. ProvisionalPatent Applications:

U.S. Provisional Patent Application No. 61/168,732, entitled “80 MHzOFDM for WLAN,” filed on Apr. 13, 2009;

U.S. Provisional Patent Application No. 61/181,518, entitled “80 MHzOFDM for WLAN,” filed May 27, 2009;

U.S. Provisional Patent Application No. 61/227,360, entitled “80 MHzOFDM for WLAN,” filed Jul. 21, 2009;

U.S. Provisional Patent Application No. 61/228,911, entitled “80 MHzOFDM for WLAN,” filed Jul. 27, 2009;

U.S. Provisional Patent Application No. 61/229,900, entitled “80 MHzOFDM for WLAN,” filed Jul. 30, 2009;

U.S. Provisional Patent Application No. 61/232,724, entitled “80 MHzOFDM for WLAN,” filed Aug. 10, 2009;

U.S. Provisional Patent Application No. 61/233,440, entitled “80 MHzOFDM for WLAN,” filed Aug. 12, 2009;

U.S. Provisional Patent Application No. 61/234,943, entitled “80 MHzOFDM for WLAN,” filed Aug. 18, 2009;

U.S. Provisional Patent Application No. 61/240,604, entitled “80 MHzOFDM for WLAN,” filed Sep. 8, 2009;

U.S. Provisional Patent Application No. 61/240,945, entitled “80 MHzOFDM for WLAN,” filed Sep. 9, 2009;

U.S. Provisional Patent Application No. 61/241,760, entitled “80 MHzOFDM for WLAN,” filed Sep. 11, 2009;

U.S. Provisional Patent Application No. 61/244,779, entitled “80 MHzOFDM for WLAN,” filed Sep. 22, 2009;

U.S. Provisional Patent Application No. 61/252,290, entitled “80 MHzOFDM for WLAN,” filed Oct. 16, 2009; and

U.S. Provisional Patent Application No. 61/319,773, entitled “NDPPreamble,” filed Mar. 31, 2010.

The disclosures of all of the above-referenced patent applications arehereby incorporated by reference herein in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilizeorthogonal frequency division multiplexing (OFDM).

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, and the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps. Work has begun on anew standard, IEEE 802.11ac, that promises to provide even greaterthroughput.

SUMMARY

According to one embodiment, a method for generating a data unit fortransmission via a communication channel, wherein the data unit conformsto a first communication protocol, includes generating a preamble of thedata unit. The preamble includes a first field having information thatindicates a duration of the data unit, the first field being formattedsuch that the first field is decodable by a receiver device thatconforms to a second communication protocol but does not conform to thefirst communication protocol to determine the duration of the data unitbased on the first field. Additionally, the preamble is formatted suchthat a portion of the preamble is decodable by a receiver device thatconforms to a third communication protocol but does not conform to thefirst communication protocol. Also, the preamble is formatted such thata receiver device that conforms to the first communication protocol candetermine that the data unit conforms to the first communicationprotocol. The method further includes generating a data portion of thedata unit that conforms to the first communication protocol and does notconform to either (i) the second communication protocol or (ii) thethird communication protocol.

In other embodiments, one or more of the following features are alsoincluded.

A portion of the data unit that is decodable by the receiver device thatconforms to the third communication protocol but does not conform to thefirst communication protocol includes the first field, and wherein thefirst field is formatted such that the first field is decodable by thereceiver device that conforms to the third communication protocol butdoes not conform to the first communication protocol to determine theduration of the data unit based on the first field.

The first field of the preamble includes a rate subfield and a lengthsubfield that indicate the duration of the data unit.

The first field of the preamble includes a subfield that is set to avalue that contradicts the second communication protocol. The value ofthe first subfield that contradicts the second communication protocolindicates to the receiver device that conforms to the firstcommunication protocol that the data unit conforms to the firstcommunication protocol.

A second field of the preamble includes a subfield that is set to avalue that contradicts the third communication protocol. The subfieldthat is set to the value that contradicts the third communicationprotocol indicates to the receiver device that conforms to the thirdcommunication protocol to the wait until the energy of the data unitdrops out before switching to a clear channel assessment (CCA) mode.

A second field of the preamble includes information that indicates theduration of the data unit, and wherein the portion of the preamble thatis decodable by the receiver device that conforms to the thirdcommunication protocol but does not conform to the first communicationprotocol includes the second field.

A second field of the preamble is modulated using a modulation differentthan specified by the third communication protocol. The modulation ofthe second field different than specified by the third communicationprotocol indicates to the receiver device that conforms to the firstcommunication protocol that the data unit conforms to the firstcommunication protocol.

The data portion includes data for only a single receiver device.

The data portion includes independent data for a plurality of receiverdevices.

The data portion has a cumulative bandwidth greater than a bandwidthspecified by the second communication protocol and a maximum bandwidthspecified by the third communication protocol.

The second communication protocol is the Institute for Electrical andElectronics Engineers (IEEE) 802.11a Standard.

The third communication protocol is the IEEE 802.11n Standard.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment;

FIGS. 2A and 2B are diagrams of a prior art data unit format;

FIG. 3 is a diagram of another prior art data unit format;

FIG. 4 is a diagram of another prior art data unit format;

FIG. 5 is a diagram of an example data unit format, according to anembodiment;

FIG. 6 is a diagram of another example data unit format, according to anembodiment;

FIG. 7A are diagrams of modulation used to modulate symbols in a priorart data unit;

FIG. 7B are diagrams of modulation used to modulate symbols in anexample data unit, according to an embodiment;

FIG. 7C are diagrams of modulation used to modulate symbols in anotherexample data unit, according to an embodiment;

FIG. 7D are diagrams of modulation used to modulate symbols in anotherexample data unit, according to an embodiment;

FIG. 7E is a diagram of modulation used to modulate a symbol in anotherexample data unit, according to an embodiment;

FIG. 8 is a diagram of tones in an orthogonal frequency divisionmultiplexing (OFDM) symbol, according to an embodiment;

FIG. 9 is a diagram of another example data unit format, according to anembodiment;

FIG. 10 is a diagram of another example data unit format, according toan embodiment;

FIG. 11 is a diagram of another example data unit format, according toan embodiment;

FIGS. 12A and 12B are diagrams of modulation used to modulate symbols intwo example data units, according to an embodiment;

FIG. 13 is a diagram of another example data unit format, according toan embodiment;

FIG. 14 is a diagram of another example data unit format, according toan embodiment;

FIG. 15 is a diagram of another example data unit format, according toan embodiment;

FIG. 16 is a diagram of an example field used in a data unit, accordingto an embodiment;

FIG. 17 is a diagram of another example data unit format, according toan embodiment;

FIG. 18 is a diagram of another example data unit format, according toan embodiment;

FIG. 19 is a diagram of another example data unit format, according toan embodiment;

FIG. 20 is a diagram of another example data unit format, according toan embodiment;

FIG. 21A is a diagram of another example data unit, according to anembodiment;

FIG. 21B are diagrams of modulation used to modulate symbols in theexample data unit of FIG. 21A, according to an embodiment;

FIG. 22 is a diagram of another example data unit, according to anembodiment;

FIG. 23 is a diagram of an example sounding data unit, according to anembodiment; and

FIG. 24 is a diagram of another example sounding data unit, according toan embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. The AP is configured to operatewith client stations according to at least a first communicationprotocol. Similarly, different client stations in the vicinity of the APmay be configured to operate according to different communicationprotocols. When the AP transmits a data unit according to a firstprotocol, a preamble of the data is formatted such that a client stationthat operates according to a second protocol, and not the firstprotocol, is able to determine certain information regarding the dataunit, such as a duration of the data unit, and/or that the data unitdoes not conform to the second protocol. Additionally, a preamble of thedata unit is formatted such that a client station that operatesaccording to the first protocol is able to determine the data unitconforms to the first protocol. Similarly, a client station configuredto operate according to the first protocol also transmits data unitssuch as described above.

Data units formatted such as described above may be useful, for example,with an AP that is configured to operate with client stations accordingto a plurality of different communication protocols and/or with WLANs inwhich a plurality of client stations operate according to a plurality ofdifferent communication protocols. Continuing with the example above, acommunication device configured to operate according to both the firstcommunication protocol and the second communication protocol is able todetermine that the data unit is formatted according to the firstcommunication protocol and not the second communication protocol.Similarly, a communication device configured to operate according to thesecond communication protocol but not the first communication protocolis able to determine that the data unit is not formatted according tothe second communication protocol and/or determine a duration of thedata unit.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) unit 18 and a physical layer(PHY) unit 20. The PHY unit 20 includes a plurality of transceivers 21,and the transceivers are coupled to a plurality of antennas 24. Althoughthree transceivers 21 and three antennas 24 are illustrated in FIG. 1,the AP 14 can include different numbers (e.g., 1, 2, 4, 5, etc.) oftransceivers 21 and antennas 24 in other embodiments. In one embodiment,the MAC unit 18 and the PHY unit 20 are configured to operate accordingto a first communication protocol (e.g., the IEEE 802.11ac Standard, nowin the process of being standardized). In another embodiment, the MACunit 18 and the PHY unit 20 are also configured to operate according toa second communication protocol (e.g., the IEEE 802.11n Standard). Inyet another embodiment, the MAC unit 18 and the PHY unit 20 areadditionally configured to operate according to the second communicationprotocol and a third communication protocol (e.g., the IEEE 802.11aStandard).

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 can includedifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. At least one of the client stations25 (e.g., client station 25-1) is configured to operate at leastaccording to the first communication protocol. In some embodiments, atleast one of the client stations 25 is not configured to operateaccording to the first communication protocol but is configured tooperate according to at least one of the second communication protocolor the third communication protocol (referred to herein as a “legacyclient station”).

The client station 25-1 includes a host processor 26 coupled to anetwork interface 27. The network interface 27 includes a MAC unit 28and a PHY unit 29. The PHY unit 29 includes a plurality of transceivers30, and the transceivers 30 are coupled to a plurality of antennas 34.Although three transceivers 30 and three antennas 34 are illustrated inFIG. 1, the client station 25-1 can include different numbers (e.g., 1,2, 4, 5, etc.) of transceivers 30 and antennas 34 in other embodiments.

In an embodiment, one or both of the client stations 25-2 and 25-3, hasa structure the same as or similar to the client station 25-1. In anembodiment, the client station 25-4, has a structure similar to theclient station 25-1. In these embodiments, the client stations 25structured the same as or similar to the client station 25-1 have thesame or a different number of transceivers and antennas. For example,the client station 25-2 has only two transceivers and two antennas,according to an embodiment.

According to an embodiment, the client station 25-4 is a legacy clientstation, i.e., the client station 25-4 is not enabled to receive andfully decode a data unit that is transmitted by the AP 14 or anotherclient station 25 according to the first communication protocol.Similarly, according to an embodiment, the legacy client station 25-4 isnot enabled to transmit data units according to the first communicationprotocol. On the other hand, the legacy client station 25-4 is enabledto receive and fully decode and transmit data units according to thesecond communication protocol and/or the third communication protocol.

In various embodiments, the PHY unit 20 of the AP 14 is configured togenerate data units conforming to the first communication protocol andhaving formats described hereinafter. The transceiver(s) 21 is/areconfigured to transmit the generated data units via the antenna(s) 24.Similarly, the transceiver(s) 24 is/are configured to receive the dataunits via the antenna(s) 24. The PHY unit 20 of the AP 14 is configuredto process received data units conforming to the first communicationprotocol and having formats described hereinafter and to determine thatsuch data units conform to the first communication protocol, accordingto various embodiments.

In various embodiments, the PHY unit 29 of the client device 25-1 isconfigured to generate data units conforming to the first communicationprotocol and having formats described hereinafter. The transceiver(s) 30is/are configured to transmit the generated data units via theantenna(s) 34. Similarly, the transceiver(s) 30 is/are configured toreceive data units via the antenna(s) 34. The PHY unit 29 of the clientdevice 25-1 is configured to process received data units conforming tothe first communication protocol and having formats describedhereinafter and to determine that such data units conform to the firstcommunication protocol, according to various embodiments.

FIG. 2A is a diagram of a prior art data unit 60 that the legacy clientstation 25-4 is configured to transmit to the AP 14 via orthogonalfrequency domain multiplexing (OFDM) modulation, according to anembodiment. The data unit 60 conforms to the IEEE 802.11a Standard andoccupies a 20 Megahertz (MHz) band. The data unit 60 includes a preamblehaving a legacy short training field (L-STF) 62, a legacy long trainingfield (L-LTF) 64, and a legacy signal field (L-SIG) 66. The data unit 60also includes a data portion 68. FIG. 2B is a diagram of an example dataportion 68 (not low density parity check encoded), which includes aservice field, a scrambled physical layer service data unit (PSDU), tailbits, and padding bits, if needed.

FIG. 3 is a diagram of a prior art OFDM data unit 78 that the legacyclient station 25-4 is configured to transmit to the AP 14, according toan embodiment. The data unit 78 conforms to the IEEE 802.11n Standard,occupies a 20 MHz band, and is designed for mixed mode situations, i.e.,when the WLAN includes one or more client stations that conform to theIEEE 802.11a Standard but not the IEEE 802.11n Standard. The data unit78 includes a preamble having an L-STF 80, an L-LTF 81, an L-SIG 82, ahigh throughput signal field (HT-SIG) 83, a high throughput shorttraining field (HT-STF) 84, N data high throughput long training fields(HT-LTFs) 85, where N is an integer, and M extension HT-LTFs 86, where Mis an integer. The data unit 78 also includes a data portion 87.

FIG. 4 is a diagram of a prior art OFDM data unit 90 that the legacyclient station 25-4 is configured to transmit to the AP 14, according toan embodiment. The data unit 90 conforms to the IEEE 802.11n Standard,occupies a 20 MHz band, and is designed for “Greenfield” situations,i.e., when the WLAN does not include any client stations that conform tothe IEEE 802.11a Standard but not the IEEE 802.11n Standard. The dataunit 90 includes a preamble having a high throughput Greenfield shorttraining field (HT-GF-STF) 91, a first high throughput long trainingfield (HT-LTF1) 92, a HT-SIG 93, N data HT-LTFs 94, where N is aninteger, and M extension HT-LTFs 95, where M is an integer. The dataunit 90 also includes a data portion 98.

FIG. 5 is a diagram of an OFDM data unit 100 that the AP 14 isconfigured to transmit to the client station 25-1, according to anembodiment. In an embodiment, the client station 25-1 is also configuredto transmit the data unit 100 to the AP 14. The data unit 100 conformsto the first communication protocol and occupies an 80 MHz band. Inother embodiments, data units similar to the data unit 100 occupydifferent bandwidths such as 20 MHz, 40 MHz, 120 MHz, 160 MHz, or anysuitable bandwidth. Additionally, the 80 MHz band need not becontiguous, but may include two or more smaller bands, such as two 40MHz bands, separated in frequency. The data unit 100 is suitable for“mixed mode” situations, i.e., when the WLAN 10 includes a clientstation (i.e., the legacy client station 25-4) that conforms to the IEEE802.11a Standard and/or the IEEE 802.11n Standard, but not the firstcommunication protocol. The data unit 100 can be utilized in othersituations as well. The data unit 100 includes a preamble having fourL-STFs 104, four L-LTFs 108, four L-SIGs 112, four first very highthroughput signal fields (VHT-SIG1) 116, four second very highthroughput signal fields (VHT-SIG2) 120, a very high throughput shorttraining field (VHT-STF) 124, and N very high throughput long trainingfields (VHT-LTFs) 128, where N is an integer. The data unit 100 alsoincludes a data portion 140. The L-STFs 104, the L-LTFs 108, and theL-SIGs 112 form a legacy portion. The VHT-STF 124, the VHT-LTFs 128, andthe data portion 140 form a very high throughput (VHT) portion.

In the embodiment of FIG. 5, each of the L-STFs 104, each of the L-LTFs108, each of the L-SIGs 112, each of the VHT-SIG1s, and each of theVHT-SIG2s occupy a 20 MHz band. In the present disclosure, severalexample data units, including the data unit 100, having an 80 MHzcontiguous bandwidth are described for the purposes of illustratingembodiments of frame formats, but these frame format embodiments andother embodiments are applicable to other suitable bandwidths (includingnoncontiguous bandwidths). For instance, although the preamble of FIG. 5includes four of each of the L-STFs 104, the L-LTFs 108, the L-SIGs 112,the VHT-SIG1s, and the VHT-SIG2s, in other embodiments in which the OFDMdata unit occupies a cumulative bandwidth other than 80 MHz, such as 20MHz, 40 MHz, 120 MHz, 160 MHz, etc., a different suitable number of theL-STFs 104, the L-LTFs 108, the L-SIGs 112, the VHT-SIG1s, and theVHT-SIG2s is utilized accordingly (e.g., one of each of the L-STFs 104,the L-LTFs 108, the L-SIGs 112, the VHT-SIG1s, and the VHT-SIG2s for anOFDM data unit occupying 20 MHz, two of each of the fields for a 40 MHzbandwidth OFDM data unit, six of each of the fields for a 120 MHzbandwidth OFDM data unit, and eight of each of the fields for a 160 MHzbandwidth OFDM data unit). Also in 80 MHz and 160 MHz bandwidth OFDMdata units, for example, the band is not contiguous in frequency, insome embodiments and situations. Thus, for example, the L-STFs 104, theL-LTFs 108, the L-SIGs 112, the VHT-SIG1s, and the VHT-SIG2s occupy twoor more bands that are separated from each other in frequency, andadjacent bands are separated in frequency by at least one MHz, at leastfive MHz, at least 10 MHz, at least 20 MHz, for example, in someembodiments. In the embodiment of FIG. 5, each of the STF 124, theVHT-LTFs 128, and the data portion 140 occupy an 80 MHz band. If thedata unit conforming to the first communication protocol is an OFDM dataunit that occupies a cumulative bandwidth such as 20 MHz, 40 MHz, 120MHz, or 160 MHz OFDM, the VHT-STF, VHT-LTFs and VHT data portion occupythe corresponding whole bandwidth of the data unit, according to anembodiment.

In an embodiment, each of the L-STFs 104 and each of the L-LTFs 108 havea format as specified in the IEEE 802.11a Standard and/or the IEEE802.11n Standard. In an embodiment, each of the L-SIGs 112 has a formatat least substantially as specified in the IEEE 802.11a Standard and/orthe IEEE 802.11n Standard. The length and rate subfields in the L-SIGs112 are set to indicate the duration T corresponding to remainder of thedata unit 100 after the legacy portion. This permits client devices thatare not configured according to the first communication protocol todetermine an end of the data unit 100, for carrier sense multipleaccess/collision avoidance (CSMA/CA) purposes, for example. Forinstance, a legacy client device configured according to the IEEE802.11a Standard will detect a data error from VHT-SIG1 field, accordingto the receiver state machine specified in the IEEE 802.11a Standard.Further according to the IEEE 802.11a Standard, the legacy client devicewill wait until the end of a computed packet duration (T) beforeperforming clear channel assessment (CCA).

The frequency domain symbols of the legacy portion are repeated overfour 20 MHz sub-bands of the 80 MHz band. Legacy client devices that areconfigured according to the IEEE 802.11a Standard and/or the IEEE802.11n Standard with 20 MHz bandwidth will recognize a legacy IEEE802.11a Standard preamble in any of the 20 MHz sub-bands. In someembodiments, the modulation of different 20 MHz sub-bands signals isrotated by different angles. For example, in one embodiment, a firstsubband is rotated 0-degrees, a second subband is rotated 90-degrees, athird sub-band is rotated 180-degrees, and a fourth sub-band is rotated270-degrees. In other embodiments, different suitable rotations areutilized. As just one example, a first sub-band is rotated 45-degrees, asecond sub-band is rotated 90-degrees, a third sub-band is rotated−45-degrees, and a fourth sub-band is rotated −90-degrees.

In one embodiment, each of the L-SIGs 112 has a format at leastsubstantially as specified in the IEEE 802.11a Standard and/or the IEEE802.11n Standard except that the “reserved” bit is set to 1, whereas theIEEE 802.11a Standard and the IEEE 802.11n Standard specify that the“reserved” bit is set to 0. By setting the “reserved” bit to 1, thissignals devices that conform to the first communication protocol thatthe data unit 100 conforms to the first communication protocol, forexample. In other embodiments, the “reserved” bit to 0.

In one embodiment, each of the VHT-SIG1s, and each of the VHT-SIG2s hasa format at least substantially the same as the HT-SIG1 and the HT-SIG2fields specified in the IEEE 802.11n Standard. For example, a modulationand coding scheme (MCS) field in VHT-SIG1 and/or VHT-SIG2 is the same asthe MCS field in HT-SIG, but applied to an 80 MHz band. In oneembodiment, MCS 32 is disallowed for VHT data units such as the dataunit 100. In other embodiments, MCS 32 is allowed for VHT data unitssuch as the data unit 100.

In some embodiments, the format and/or modulation of VHT-SIG1 and/orVHT-SIG2 is at least different to cause a legacy device operatingaccording to the IEEE 802.11n Standard to detect an error, such as acyclic redundancy check (CRC) error. Further according to the IEEE802.11n Standard, the legacy client device will wait until the energy ofthe data unit 100 drops out before switching to CCA idle mode.

In some embodiments, the modulation of the VHT-SIG1s and/or theVHT-SIG2s in the different 20 MHz sub-bands signals is rotated bydifferent angles. For example, in one embodiment, a first sub-band isrotated 0-degrees, a second sub-band is rotated 90-degrees, a thirdsub-band is rotated 180-degrees, and a fourth sub-band is rotated270-degrees. In other embodiments, different suitable rotations areutilized. As just one example, a first sub-band is rotated 45-degrees, asecond sub-band is rotated 90-degrees, a third sub-band is rotated−45-degrees, and a fourth sub-band is rotated −90-degrees. In anembodiment, the same rotation utilized in the legacy portion (if any) isutilized for the VHT-SIG1s and the VHT-SIG2s.

In one embodiment, the “reserved” bit (as specified for HT-SIG in theIEEE 802.11n Standard) in VHT-SIG2 is set to 0, whereas the IEEE 802.11nStandard defines the reserved bit in HT-SIG is set to 1), to signal to adevice configured according to the first communication protocol that thedata unit 100 conforms to the first communication protocol. In otherembodiments, the “reserved” bit (as specified for HT-SIG in the IEEE802.11n Standard) in VHT-SIG2 is set to 1.

In some embodiments, each of the VHT-SIG1s and each of the VHT-SIG2shave a format not substantially the same as the HT-SIG1 and the HT-SIG2fields specified in the IEEE 802.11n Standard. For example, the subfieldin HT-SIG “BW20/40” as defined in the IEEE 802.11n Standard is omitted,or is combined with the reserved bit to select 20, 40, or 80 MHzbandwidth, according to an embodiment. As another example, the subfield“aggregated” as defined in the IEEE 802.11n Standard is omitted. In anembodiment, differences in the formats of the VHT-SIG fields and theHT-SIG fields defined in the IEEE 802.11n Standard will cause a legacydevice configured according to the IEEE 802.11n Standard to detect anerror, such as a CRC error, upon receiving a VHT-SIG field.

FIG. 6 a diagram of an OFDM data unit 150 that the AP 14 is configuredto transmit to the client station 25-1, according to an embodiment. Inan embodiment, the client station 25-1 is also configured to transmitthe data unit 150 to the AP 14. The data unit 150 is the same as thedata unit 100 of FIG. 5, except that the data unit 150 includes thirdvery high throughput signal fields (VHT-SIG3s) 154 to convey physicallayer (PHY) information. In the embodiment of FIG. 6, a CRC may covereach VHT-SIG1, VHT-SIG3, VHT-SIG3 tuple. In an embodiment, the CRC thatcovers the VHT-SIG1, VHT-SIG3, VHT-SIG3 tuple is the same as defined forHT-SIG in the IEEE 802.11n Standard.

In an embodiment, the 3 VHT-SIG subfield formats are substantiallydifferent from HT-SIG fields in the IEEE 802.11n Standard (e.g. use 2bits to signal 20/40/80 MHz bandwidth, or no indication of 20/40/80 MHzin an implementation that only 80 MHz is allowed for VHT packets). In anembodiment, the same CRC check as in HT-SIG specified by the IEEE802.11n Standard is moved to VHT-SIG3, and the CRC checks thecorrectness of the data in all the 3 VHT-SIG fields.

FIG. 7A is a set of diagrams illustrating modulation of the L-SIG,HT-SIG1, and HT-SIG2 fields as defined by the IEEE 802.11n Standard. TheL-SIG field is modulated according to binary phase shift keying (BPSK),whereas the HT-SIG1 and HT-SIG2 fields are modulated according to BPSK,but on the quadrature axis (Q-BPSK). In other words, the modulation ofthe HT-SIG1 and HT-SIG2 fields is rotated by 90 degrees as compared tothe modulation of the L-SIG field.

FIG. 7B is a set of diagrams illustrating modulation of the L-SIG,VHT-SIG1, and VHT-SIG2 fields of the data unit 100 of FIG. 5, accordingto an embodiment. Similar to the HT-SIG1 field in FIG. 7A, the VHT-SIG1field is rotated by 90 degrees as compared to the modulation of theL-SIG field. On the other hand, unlike the HT-SIG2 field of FIG. 7A, theVHT-SIG2 field is the same as the modulation of the L-SIG field. In anembodiment, the different modulation of the VHT-SIG2 field and theHT-SIG2 field defined in the IEEE 802.11n Standard will cause a legacydevice configured according to the IEEE 802.11n Standard to detect anerror, such as a CRC error, upon receiving a VHT-SIG2 field.Additionally, the different modulation of the VHT-SIG2 field and theHT-SIG2 field defined in the IEEE 802.11n Standard will permit a deviceconfigured according to the first communication protocol to determinethat the data unit 100 conforms to the first communication protocol.

In other embodiments, the VHT-SIG2 field is rotated by 90 degrees ascompared to the modulation of the L-SIG field, similar to the HT-SIG2field of FIG. 7A.

FIG. 7C is a set of diagrams illustrating modulation of the L-SIG,VHT-SIG1, VHT-SIG2, and VHT-SIG3 fields of the data unit 150 of FIG. 6,according to an embodiment. Similar to the HT-SIG1 field in FIG. 7A, theVHT-SIG1 field is rotated by 90 degrees as compared to the modulation ofthe L-SIG field. On the other hand, unlike the HT-SIG2 field of FIG. 7A,the VHT-SIG2 field is the same as the modulation of the L-SIG field.Additionally, the VHT-SIG3 field is the same as the modulation of theL-SIG field. In an embodiment, the different modulation of the VHT-SIG2field and the HT-SIG2 field defined in the IEEE 802.11n Standard willcause a legacy device configured according to the IEEE 802.11n Standardto detect an error, such as a CRC error, upon receiving a VHT-SIG2field. Additionally, the different modulation of the VHT-SIG2 field andthe HT-SIG2 field defined in the IEEE 802.11n Standard will permit adevice configured according to the first communication protocol todetermine that the data unit 150 conforms to the first communicationprotocol.

In other embodiments, the VHT-SIG2 field is rotated by 90 degrees ascompared to the modulation of the L-SIG field, similar to the HT-SIG2field of FIG. 7A. In other embodiments, the VHT-SIG3 field is rotated by90 degrees as compared to the modulation of the L-SIG field.

Referring to FIGS. 5 and 6, each VHT-SIG is modulated by one OFDMsymbol, according to an embodiment.

If the VHT-SIG fields in the data units as described in FIGS. 5 and 6,utilizes the modulations as described in FIGS. 7B and 7C, in theseembodiments, a device that conforms to the IEEE 802.11a Standard willset CCA idle duration according to the L-SIG field. A device thatconforms to the IEEE 802.11n Standard (also compatible with the IEEE802.11a Standard) will assume, at least in some circumstances, that thedata unit is a data unit that conforms to the IEEE 802.11n standard(since VHT-SIG1 is modulated the same way as HT-SIG1), but may faildecoding the assumed two “HT-SIG” fields since the VHT-SIG2 is modulateddifferent from HT-SIG2. In this case, the IEEE 802.11n conforming devicemay set CCA idle duration according to the L-SIG field, or set CCA idleduration according to the energy of the data unit (i.e. reset CCA whenthe over-the-air energy of the data unit drops down to a certainlevel—meaning the data unit ends). Devices that conform to the firstcommunication protocol will determine that the data unit conforms to thefirst communication protocol by one or more of detecting the “reservedbit” in the L-SIG field, detecting the “reserved bit” in the VHT-SIGfield, detecting modulation of the VHT-SIG fields, etc., depending onthe particular embodiment.

In some embodiment, the VHT-SIG fields are modulated differently than asshown in FIGS. 7B and 7C. In the above mentioned VHT signalingapproaches that change the constellation points of the VHT_SIG fieldslocated immediately after the L-SIG field (i.e. FIGS. 5 and 6) to signalthat the data unit conforms to the first communication protocol,generally any suitable change to the VHT-SIG fields modulation that isdifferent from modulation from the HT-SIG fields in the IEEE 802.11nStandard, or any changes on L-SIG modulation that is different fromL-SIG in the IEEE 802.11n and the IEEE 802.11n Standards can beutilized. Different from FIG. 7B or 7C, in an embodiment, any suitablemodulation in VHT-SIG1 is utilized so that a device that conforms to theIEEE 802.11n Standard will assume the data unit is not an HT data unit(e.g., the average Q energy of the constellation is not significantlylarger than 1 energy as defined in the IEEE 802.11n Standard for theHT-SIG field) but rather assumes that data unit is an IEEE 802.11a dataunit, and thus treats the data unit as an IEEE 802.11a data unit. Inthis case, although the IEEE 802.11n conforming device may not decodethe data unit correctly, it will set CCA idle duration correctlyaccording to the L-SIG field. Further, a device that conforms to thefirst communication protocol can determine that the data unit conformsto the first communication protocol by one or more of detecting the“reserved bit” in the L-SIG field, detecting the “reserved bit” in theVHT-SIG field, detecting modulation of the VHT-SIG fields, etc.,depending on the particular embodiment.

For example, in one embodiment, all of the VHT-SIG symbols are modulatedusing BPSK. As another example, the first VHT-SIG symbol is BPSK, andthe remaining symbols are modulated using Q-BPSK. FIG. 7D is a set ofdiagrams illustrating modulation of the L-SIG, VHT-SIG1, and VHT-SIG2fields of the data unit 100 of FIG. 5, according to an embodiment.Unlike the HT-SIG1 field in FIG. 7A, the VHT-SIG1 field is not rotatedby 90 degrees as compared to the modulation of the L-SIG field (i.e.,the VHT-SIG1 field is BPSK modulated). On the other hand, like theHT-SIG2 field of FIG. 7A, the VHT-SIG2 field is rotated by 90 degrees ascompared to the modulation of the L-SIG field. In the embodiment of FIG.7D, devices conforming to the IEEE 802.11n Standard will treat the dataunit as an IEEE 802.11a data unit, because the modulation of theVHT-SIG1 field is not BPSK, as specified by the IEEE 802.11n standard.In this embodiment, the device conforming to the IEEE 802.11n Standardwill set the CCA idle duration according to L-SIG. The modulation ofFIG. 7D can also be used with the data unit 150 of FIG. 6, and FIG. 7Eis a diagram of modulation for the VHT-SIG3 field of FIG. 6, accordingto an embodiment. In another embodiment, all or the first or some of theVHT-SIG symbols are modulated with neither BPSK, nor Q-BPSK. Forexample, VHT-SIG1 or VHT-SIG2 or all the VHT-SIGs are modulated with45-deg rotated BPSK. As another example, VHT-SIG1 or VHT-SIG2 or all theVHT-SIGs are modulated with R*45-deg rotated BPSK, wherein R=1, 2, or 3.As another example, VHT-SIG1 or VHT-SIG2 or all the VHT-SIGs aremodulated with BPSK and Q-BPSK alternatively or not alternatively but ina predetermined manner (e.g. any N tones using Q-BPSK, the other 52-Ntones using BPSK) across the data and pilot tones (52 tones in each 20MHz sub-band) i.e., a predetermined mapping of the tones for BPSK andQ-BPSK modulations.

The VHT-STF, VHT-LTFs, and VHT-Data OFDM symbols are defined similar toHT-STF, HT-LTFs and HT-Data as in the IEEE 802.11n Standard, except thateach OFDM symbol is defined over 80 MHz bandwidth, according to anembodiment. In other embodiments, each OFDM symbol is defined over othersuitable bandwidths, such as 20 MHz, 40 MHz, 160 MHz, etc. In the caseof an 80 MHz OFDM symbol, a 256 point inverse fast Fourier transform(IFFT) and a 256 point fast Fourier transform (FFT) is utilized for 80MHz bandwidth transmissions. In an embodiment, the OFDM duration is 3.6microseconds (ns) for a short guard interval (GI) and 4 ns for a longGI.

If the constraint on the maximum number of space-time streams is thesame as in the IEEE 802.11n Standard, then the spatial mapping P matrixin VHT-STFs, and VHT-LTFs, signal shaping such as frequency cyclic shiftdiversity (CSD), etc., are substantially the same as the IEEE 802.11nStandard, (e.g., extended to an 80 MHz band), according to anembodiment.

For an 80 MHz OFDM signal, the symbols in the tones of VHT-STF andVHT-LTFs, the assignment of data tone numbers/positions, guard tonesaround edge bands and direct current (DC) tones, number/position/contentof pilot tones, and the frequency interleaver, are configureddifferently from 20 MHz bandwidth and 40 MHz bandwidth legacy signals inthe IEEE 802.11a Standard and the IEEE 802.11n Standard.

Pilots will not be present for VHT-STF and VHT-LTFs as in the IEEE802.11a Standard and the IEEE 802.11n Standard, according to anembodiment.

FIG. 8 is a diagram illustrating an example OFDM tone structure for an80 MHz OFDM symbol for the VHT-data portions of FIGS. 5 and 6, accordingto an embodiment. An OFDM symbol 180 includes a group 184 of zero tonesat a lower frequency end, a group 188 of zero tones at a center section,and a group 192 of zero tones at an upper frequency end. Data and pilottones are located between the groups of zero tones.

FIG. 9 is a diagram of an OFDM data unit 200 that the AP 14 isconfigured to transmit to the client station 25-1, according to anembodiment. In an embodiment, the client station 25-1 is also configuredto transmit the data unit 200 to the AP 14. The data unit 200 conformsto the first communication protocol and occupies an 80 MHz band. Inother embodiments, data units similar to the data unit 200 occupydifferent bandwidths such as 20 MHz, 40 MHz, 120 MHz, 160 MHz, or anysuitable bandwidth. Additionally, the band in which the OFDM data unitis transmitted need not be contiguous, but may include two or moresmaller bands separated in frequency. In an embodiment in which the OFDMdata unit 200 has an 80 MHz bandwidth, for example, the OFDM data unit200 may occupy two separate 40 MHz bands, separated in frequency. Thedata unit 200 is suitable for “Greenfield” situations, i.e., when theWLAN 10 does not include any client stations (i.e., the legacy clientstation 25-4) that conforms to the IEEE 802.11a Standard and/or the IEEE802.11n Standard, but not the first communication protocol. The dataunit 200 can be utilized in other situations as well. For example, issome embodiments, the data unit 200 can be utilized i.e., when the WLAN10 does not include any client stations that conforms to the IEEE802.11a Standard but not the first communication protocol, but includesone or more client stations that conform to the IEEE 802.11n Standardbut not the first communication protocol.

The data unit 200 is similar to the data unit 100 of FIG. 5, but omitsthe legacy portion. Additionally, the VHT-STF 124 and the first VHT-LTF128-1 occur before the VHT-SIG1s 116 and the VHT-SIG2s 120. Otherwise,the VHT-SIG1s 116, the VHT-SIG2s 120, the VHT-STF 124, and the VHT-LTFs128 are the same as described above with respect to FIGS. 5 and 6. Forexample, in an embodiment in which the modulations in VHT-SIG fields inFIG. 9 are as in FIG. 7B or 7C, a legacy client configured according tothe IEEE 802.11n Standard will interpret the VHT-SIG1s 116 and theVHT-SIG2s 120 as HT-SIG1s and HT-SIG2s, but will generate a CRC error.In another embodiment, when the modulations in VHT-SIG fields in FIG. 9are as in FIG. 7D, a legacy client configured according to the IEEE802.11n Standard will interpret the VHT-SIG1s 116 and the VHT-SIG2s 120as L-SIGs and HT-SIG1s respectively, but will generate a CRC error. Ingeneral, the Greenfield data unit 200 is designed for utilization in anetwork having only devices that conform to the first communicationprotocol, and not including any legacy devices. In some situations,however, the Greenfield data unit 200 may be transmitted in a networkhaving one or more legacy devices.

FIG. 10 is a diagram of an OFDM data unit 250 that the AP 14 isconfigured to transmit to the client station 25-1, according to anembodiment. In an embodiment, the client station 25-1 is also configuredto transmit the data unit 250 to the AP 14. The data unit 250 conformsto the first communication protocol and occupies an 80 MHz band. Inother embodiments, data units similar to the data unit 200 occupydifferent bandwidths such as 20 MHz, 40 MHz, 120 MHz, 160 MHz, or anysuitable bandwidth. Additionally, the 80 MHz band need not becontiguous, but may include two or more smaller bands, such as two 40MHz bands, separated in frequency. The data unit 250 is suitable for“mixed mode” situations, i.e., when the WLAN 10 includes at least oneclient station (i.e., the legacy client station 25-4) that conforms tothe IEEE 802.11a Standard and/or the IEEE 802.11n Standard, but not thefirst communication protocol. The data unit 250 can be utilized in othersituations as well. For example, is some embodiments, the data unit 250can be utilized i.e., when the WLAN 10 does not include any clientstations that conforms to the IEEE 802.11a Standard but not the firstcommunication protocol, but includes one or more client stations thatconform to the IEEE 802.11n Standard but not the first communicationprotocol.

The data unit 250 is similar to the data unit 100 of FIG. 5, butincludes HT-SIG1s 254 and HT-SIG2s 258. Further, the rate and lengthfields in the L-SIGs are set according to the duration T1, whichincludes the HT-SIG1s 254 and the HT-SIG2s 258.

In an embodiment, the “HT-Length” field, the “MCS” field, the space-timecoding block (STBC) field, etc., in the HT-SIG1 254 are set so that adevice configured according to the IEEE 802.11n Standard will computethe true duration of the data unit 250. In an embodiment, the “reserved”bit in the HT-SIG1s 254 and/or the HT-SIG2s 258 is set to “0” to signaldevices that conform to the first communication protocol that the dataunit 250 conforms to the first communication protocol. Additionally,when the “reserved” bit in the HT-SIG2s 258 is set to “0”, a deviceconfigured according to the IEEE 802.11n Standard will determine“carrier lost” after decoding HT-SIG2. According to the state machinedefined in the IEEE 802.11n Standard, the 802.11n device will hold CCAuntil the end of the duration computed according to the “HT-Length”field, the “MCS” field, the STBC field, etc.

The VHT-SIG1s 116 and the VHT-SIG2s 120 have a different format than theHT-SIG1s 254 and the HT-SIG2s 258, in an embodiment.

FIG. 11 is a diagram of an OFDM data unit 270 that the AP 14 isconfigured to transmit to the client station 25-1, according to anembodiment. In an embodiment, the client station 25-1 is also configuredto transmit the data unit 270 to the AP 14. The data unit 250 conformsto the first communication protocol and occupies an 80 MHz band. Inother embodiments, data units similar to the data unit 200 occupydifferent bandwidths such as 20 MHz, 40 MHz, 120 MHz, 160 MHz, or anysuitable bandwidth. Additionally, the 80 MHz band need not becontiguous, but may include two or more smaller bands, such as two 40MHz bands, separated in frequency. The data unit 270 is suitable for“mixed mode” situations in which the WLAN 10 includes at least oneclient station (i.e., the legacy client station 25-4) that conforms tothe IEEE 802.11n Standard, but not the first communication protocol, butthe WLAN 10 does not include any client stations that conforms to theIEEE 802.11a Standard but not IEEE 802.11n Standard and not the firstcommunication protocol. The data unit 270 can be utilized in othersituations as well.

The data unit 270 is similar to the data unit 200 of FIG. 9, butincludes HT-SIG1s 274 and HT-SIG2s 278. The HT-SIG1s 274 and HT-SIG2s278 are configured the same as the HT-SIG1s 254 and HT-SIG2s 258described with reference to FIG. 10, according to an embodiment. TheVHT-SIG1s 116 and the VHT-SIG2s 120 have a different format than theHT-SIG1s 274 and the HT-SIG2s 278, in an embodiment.

The example data unit formats and signaling approaches (e.g., L-SIGsubfield (reserved bit) changes from the IEEE 802.11a and the IEEE802.11n Standards, VHT-SIG subfield changes, and modulation changes fromHT-SIG in the IEEE 802.11n Standard) described in this disclosure may beused to signal to a device that conforms to the first communicationprotocol that the data unit conforms to the first communicationprotocol, that the data unit includes VHT-SIG fields, etc. For dataunits that conform to the first communication protocol and have abandwidth less than 80 MHz (e.g., 40 MHz or 20 MHz), such data units canutilize a similar preamble. For 40 MHz wide data units, the data unitpreamble that conforms to the first communication protocol has an upperfrequency and lower frequency duplication structure similar to or thesame as described in the IEEE 802.11n Standard, according to anembodiment.

In some embodiments similar to the embodiments described above withrespect to FIGS. 5, 6, and 10, the “Rate” subfield in the L-SIG field isset to “1101” to indicate 6 megabits per second (Mbps), and the and set“Length” subfield is set according to T or T1, for legacy devicespoofing. In these embodiments, a device that conforms to the IEEE802.11a Standard will set CCA idle duration according to the L-SIGfield. A device that conforms to the IEEE 802.11n Standard (alsocompatible with the IEEE 802.11a Standard) will assume that the dataunit is a data unit that conforms to the IEEE 802.11a Standard, and willset CCA idle duration according to the L-SIG field. Devices that conformto the first communication protocol will determine that the data unitconforms to the first communication protocol by one or more of detectingthe “reserved bit” in the L-SIG field, detecting the “reserved bit” inthe VHT-SIG field, detecting modulation of the VHT-SIG fields, etc.,depending on the particular embodiment.

In an embodiment in which the VHT-SIG1 field is modulated using BPSK asin FIG. 7D, a station that conforms to the first communication protocolwill determine that the data unit does not conform to the IEEE 802.11nStandard, and that the current packet could be either an IEEE 802.11adata unit or a data unit that conforms to the first communicationprotocol. A station that conforms to the first communication protocolwill determine that the OFDM symbol at the position of VHT-SIG1 could beeither IEEE 802.11a data or a VHT-SIG1 conforming to the firstcommunication protocol, but both are modulated using 6 Mbps (asindicated by L-SIG).

In embodiments in which signaling in VHT-SIG2 is utilized, after astation that conforms to the first communication protocol detects thatthe data unit conforms to the first communication protocol at VHT-SIG2(e.g., with the modulation of FIG. 7D, in an embodiment), the devicecombines VHT-SIG1 and VHT-SIG2 decoded bits to check CRC and get PHYparameters, according to an embodiment.

In some embodiments, MAC protection of transmission of Greenfield dataunits are utilized within a basic service set (BSS).

If there are two or three OFDM symbols in VHT-SIG (e.g., a VHT-SIG1 anda VHT-SIG2, and a VHT-SIG3 in some embodiments), a device conforming tothe first communication protocol can differentiate a green field dataunit such as shown in FIGS. 9 and 11 from an IEEE 802.11n Standard mixedmode data unit, by comparing the modulations at the position of VHT-SIGfields, according to some embodiments.

In some embodiments, VHT-SIG modulation in mixed mode and Greenfieldmode are different. FIGS. 12A and 12B are diagrams that illustratemodulation of the VHT-SIG fields in mixed mode and Greenfield mode,respectively, according to one embodiment. In the embodiment of FIGS.12A and 12B, VHT-SIG1 and VHT-SIG2 are modulated using BPSK and Q-BPSK,respectively, in mixed mode, whereas VHT-SIG1 and VHT-SIG2 are modulatedusing Q-BPSK and BPSK, respectively, in Greenfield mode. FIGS. 12A and12B may be applied for the modulations of the VHT-SIG fields in FIGS. 5and 6 for mixed mode, and FIGS. 9 and 11 for Greenfield.

In the above mentioned VHT signaling (i.e., signaling a data unitconforms to the first communication protocol) approaches in nonHT-spoofing modes (i.e., not spoofing IEEE 802.11n Standard data units),and in some embodiments, the modulations of VHT_SIG fields are the sameas the HT_SIG fields in the IEEE 802.11n Standard, but the content ofVHT_SIG fields will be different from HT-SIG of the IEEE 802.11nStandard, so that a device conforming to the IEEE 802.11n Standard willdetermine an error in the IEEE 802.11n Standard CRC check of the VHT-SIGfields (i.e., the IEEE 802.11n Standard device will perform a CRC checkon the VHT-SIG fields assuming they are HT-SIG fields). For example, inone embodiment, more than 2 VHT-SIG symbols are utilized, so the CRC forthe first communication protocol is redesigned to cover all of the morethan two VHT-SIG fields. In another embodiment, theposition/length/coding method (e.g. the initial states of the CRC logic)of the CRC bits in VHT-SIG1 and 2 are replaced, and the content of theVHT-SIG fields is different from HT-SIG fields.

In some embodiments, the VHT-STF and/or one or more VHT-LTF symbols maybe repeated two or more times (e.g., for the purpose of more reliablechannel estimation, frequency synchronization, automatic gain control(AGC) refinements, etc.). For example, in Greenfield mode data units,the VHT-STF and the first VHT-LTF symbol may be repeated two times eachas shown in FIG. 13, which is preamble 300, according to an embodiment.The preamble 300 is similar to the preamble of FIG. 9, but includes twoVHT-STFs 124-1, 124-2, two VHT-SIG1s, 128-1 a, 128-1 b, and M VHT-SIGfields, where M is an integer greater than or equal to two.

In some embodiments, the VHT-STF and/or one or more VHT-LTF symbols maybe extended beyond 4 μs. For example, in some embodiments, the VHT-STFis extended to 8 μs. FIG. 14 is a Fig diagram of an OFDM data unit 330that the AP 14 is configured to transmit to the client station 25-1,according to an embodiment. The data unit 330 is similar to the dataunit 100 of FIG. 5, but with a VHT-STF field 334 that is extended to 8μs. Additionally, in some embodiment, a cyclic prefix (CP) of one ormore VHT-LTF symbols is extended to 1.6 μs. FIG. 15 is a diagram of anOFDM data unit 340 that the AP 14 is configured to transmit to theclient station 25-1, according to an embodiment. The data unit 340 issimilar to the data unit 330 of FIG. 14, but with a first VHT-LTF field344 that includes a CP extended to 1.6 μs. In some embodiments,repetition of VHT-STF and/or VHT-LTFs is similar to repetition of theL-LTF field as described in the IEEE 802.11n Standard. For example, asingle CP (e.g. 0.8 μs) or double-length CP (1.6 μs) is followed by tworepetitions of an OFDM symbol of VHT-STF or VHT-LTF. FIG. 16 is adiagram illustrating repetition of two VHT-LTF symbols with a single CPfor the two VHT-LTF symbols. The CP is 0.8 μs in some embodiments, andis 1.6 μs in other embodiments.

In some embodiments, the training sequences used for the VHT-STF and theVHT-LTFs are defined differently from those in the IEEE 802.11nStandard. For example, if in VHT-STF and/or VHT-LTF, a pilot P_(s,n)^((k)) is transmitted on the k-th subcarrier for the n-th trainingsymbol at the s-th spatial stream, the VHT-STF and/or the VHT-LTF can beexpressed as (expression before spatial mapping) P^((k))s(k), where s(k)is the training STF or LTF symbol at the k-th subcarrier. The matrixP^((k)) used for the k-th subcarrier may be any invertible matrix thatis known at both the transmitter and the receiver. As just one exampleof a P matrix, the P vectors for different streams are interleaved inthe same VHT-LTF. In another example of a P matrix, in the embodiment ofrepeated VHT-STFs and/or VHT-LTFs, columns of the P matrix are repeatedx times, if x-time repetition is applied for the VHT-STFs or VHT-LTFs.

In some embodiments, one or more of space division multiple access(SDMA), orthogonal frequency domain multiple access (OFDMA), etc., maybe utilized in the first communication protocol. In these embodiments,one or more VHT-SIG fields contain subfield(s) that indicate whether thedata unit is part of an SDMA/OFDMA transmission (e.g., whether theVHT-SIG field corresponds to one subspace of SDMA, or one sub-band ofOFDMA). In the case of SDMA or OFDMA transmissions, all of the intendedreceivers should hold their respective CCAs until the end oftransmission of the entire data unit, and should not send acknowledgment(ACK) data units until the end of the entire data unit. Since thedifferent data streams in the data unit to the different receivers mayhave different lengths, the CCA should be held high till the end of thelongest data stream.

In an embodiment, the transmitter indicates the duration of the longestdata stream in the data unit in the LENGTH field of the L-SIG in mixedmode, or in a subfield of a VHT-SIG in Greenfield mode. The mentionedsubfield in VHT-SIG indicates to the receiver that the current packet ispart of an SDMA or OFDMA data unit, so the receiver should hold CCA forappropriate amount of time (e.g. according to the duration as indicatedin length field in L-SIG in mixed mode). In another embodiment, MACsignaling is utilized to inform the receiver of the entire length of theSDMA/OFDMA data unit.

Compared with the mixed mode preamble in the IEEE 802.11n Standard, thepreamble of at least some data units conforming to the firstcommunication protocol may be made shorter, but still backwardcompatible with the IEEE 802.11a and IEEE 802.11n Standards. In anembodiment, a Greenfield-like preamble is utilized, but with L-SIGfields inserted before the VHT-SIG fields. FIG. 17 is a diagram of anexample preamble, according to an embodiment. L-SIG fields insertedbefore the three sets of VHT-SIG fields. In another embodiment, theVHT-SIG3 fields are omitted. In the data unit 350, the modulations ofthe VHT-SIG fields is the same as those described in FIGS. 5 and 6,e.g., as illustrated in FIGS. 7B-7E, in various embodiments. In anembodiment, the spatial mapping approach of L-SIG is in the same way asVHT-SIG field (e.g. the single stream L-SIG is mapped to N_(TX) transmitantennas by a matrix QP₁, where Q is the spatial mapping matrix appliedto the VHT data, and P₁ is the first column of the P matrix asintroduced above or as in the IEEE 802.11n Standard), and themodulation/coding of L-SIG is the same as the SIG field of the IEEE802.11a Standard. In this embodiment, a receiver can use VHT-LTF1 as thechannel estimation to demodulate the L-SIG field, as it does ondemodulating VHT-SIG field for the example Greenfield mode preamblesdescribed above. In one embodiment, devices that transmit data unitsaccording to the first communication protocol utilize data unitpreambles such as in FIG. 17 for Greenfield mode. In one embodiment,“spoofing” is applied by the duration T1 (determined according to rateand length fields in L-SIG, and the reserved bit of L-SIG is set to 1 tosignal that the data unit conforms to the first communication protocol.In other embodiments, various modulation and numbers of OFDM symbols ofVHT-SIG fields, and the format/length of VHT-STF and VHT-LTF fields suchas described above are utilized.

In embodiments utilizing a preamble such as in FIG. 17, and if the LTSsymbol duplicates 20 MHz L-LTS symbols in each 20 MHz sub-band andnon-zero values are utilized in the tones corresponding to IEEE 802.11nStandard legacy “DC/Guard tones” in each sub-band of L-LTS, then areceiver, when decoding L-SIG and VHT-SIG in one or more 20 MHzsub-bands will assume an IEEE 802.11a data unit of rate 6 Mbps (assumingthe SIG fields set rate to 6 Mbps), and will determine worse channelestimation quality at tones around “DC” and “Guard band” in eachsub-band, due to the non-zero values in “DC/Guard tones” at VHT-LTF1. Inparticular, the non-zero “DC” may be more problematic.

In some embodiments, to improve the detection of SIG fields, zero valuesare kept at the “DC” tones and/or “Guard” tones in each of the sub-bandsof the LTS symbols in each of the VHT-LTF fields, and also not totransmit data in these tones in the Data field (VHT portion). In theseembodiments, SIG field decoding quality will tend to be improved, at theexpense of a lower data rate. On the other hand, a benefit of a shortmixed mode preamble compared with the other embodiments is obtained.

In some embodiments, various preamble structures such as describedabove, are modified by including one or more VHT-SIG symbols after anyVHT-LTF (e.g., VHT-LTF1, or VHT-LTF2, . . . VHT-LTFN). In someembodiments, signaling of VHT-LTF length by other VHT-SIG field(s) thatare placed after L-SIG in mixed mode, or after VHT-LTF1 in Greenfield,is utilized. In other embodiments, VHT-SIG symbols occur after VHT-LTF1.If a VHT-SIG occurs after VHT-LTFn, then it can be spatially mapped thesame way as VHT-LTFn (e.g., by vector QP_(n)) or the same way asVHT-LTF1 (e.g. by vector QP₁) so the receiver can use the channelestimation from VHT-LTFn or VHT-LTF1 to decode this VHT-SIG block afterVHT-LTFn. These techniques can be utilized in either in mixed mode orGreenfield formats. In some embodiments, a benefit is that SDMA downlinktransmissions can differentiate VHT-SIG fields for different users bybeam-steering, while keeping the legacy portion of mixed mode packetunsteered (e.g., “omni-directional”). In some embodiments, differentVHT-SIG symbols are located in unsteered and steered portions of thepreamble, such as described below.

FIG. 18 is a diagram of an example data unit 400 for use in embodimentsin which the first communication protocol supports downlink SDMA(DL-SDMA). A first portion of the data unit 400 includes L-STF, L-LTF,L-SIG, VHT-SIG1, and VHT-SIG2 fields. The first portion is transmittedomni-directional and includes the same information for all clientdevices, in an embodiment. A second portion of the data unit 400includes a VHT-STF field 401, a VHT-LTF1 field 402, a VHT-SIG3 field404, a VHT-SIG4 field 408, VHT-LTF2 through VHT-LTFN fields 412, and aVHT data portion 416. At least some of the second portion includesdifferent data for different client devices, wherein the different datais beamsteered to the different client devices.

In an embodiment, the VHT-SIG1 and VHT-SIG2 may be used to jointlysignal the number of VHT-LTFs or the number of VHT-LTFs before the nextblock of VHT-SIG for all the SDMA users. In one embodiment, content ofVHT-SIG1 and VHT-SIG2 are repetitions of L-SIG, or any other suitablesignal. In another embodiment, the VHT-SIG1 and VHT-SIG2 are anysuitable symbol that delivers any common information to all the users(e.g. common MAC information delivered from AP to all the users). Insome embodiments described herein, a first block of VHT-SIG fields (e.g.VHT-SIG1 and VHT-SIG2 in FIG. 16) is referred to as VHT-SIGA, and asecond block VHT-SIG fields (e.g. VHT-SIG3 and VHT-SIG4 in FIG. 16) isreferred to as VHT-SIGB.

In an embodiment, the “reserved” bit in L-SIG is set to 1. VHT-SIG1 andVHT-SIG2 can be modulated such as described above. If VHT-SIG1 andVHT-SIG2 are modulated using BPSK or Q-BPSK, with r=½ binaryconvolutional code (BCC), this is the same as L-SIG or HT-SIG of theIEEE 802.11n Standard. In this embodiment, the VHT-SIG1 and VHT-SIG2and/or the reserved bit in L-SIG permit spoofing and/or firstcommunication protocol data unit detection such as described above.

In an embodiment and in some scenarios, content of VHT-SIG3 and VHT-SIG4is different for different users, and is multiplexed by the steeringmatrix Q for different users.

FIG. 19 is a diagram of another example data unit 450 for use inembodiments in which the first communication protocol supports downlinkSDMA (DL-SDMA). A first portion of the data unit 450 includes L-STF,L-LTF, L-SIG, and VHT-SIG1 fields. The first portion is transmittedomni-directional and includes the same information for all clientdevices, in an embodiment. A second portion of the data unit 400includes VHT-STF, VHT-LTF1, a VHT-SIG2 field 454, a VHT-SIG3 field 458,the VHT-LTF2 through VHT-LTFN fields 412, and the VHT data portion 416.The second portion includes different data for different client devices,wherein the different data is beamsteered to the different clientdevices.

The data unit 450 is similar to the data unit 400, but one symbolshorter before the VHT-STF. In an embodiment, the “reserved” bit inL-SIG is set to 1, permitting first communication protocol data unitdetection. VHT-SIG1 can be modulated such as described above. IfVHT-SIG1 is modulated using BPSK, this permits spoofing and firstcommunication protocol data unit detection. In an embodiment, content ofVHT-SIG1 is a repetition of L-SIG, or any other suitable value.

FIG. 20 is a diagram of another example data unit 470 for use inembodiments in which the first communication protocol supports downlinkSDMA (DL-SDMA). A first portion of the data unit 470 includes L-STF,L-LTF, L-SIG, HT-SIG1, and HT-SIG2 fields. The first portion istransmitted omni-directional and includes the same information for allclient devices, in an embodiment. A second portion of the data unit 400includes VHT-STF, VHT-LTF1, a VHT-SIG1 field 474, a VHT-SIG2 field 478,the VHT-LTF2 through VHT-LTFN fields 412, and the VHT data portion 416.The second portion includes different data for different client devices,wherein the different data is beamsteered to the different clientdevices.

The data unit 470 is similar to the data unit 400, but includes HT-SIGfields in the first portion. In this embodiment, the length field inHT-SIG is used to indicate the length of the data unit 470 for IEEE802.11n spoofing.

In embodiments similar to those described above, the VHT-SIG blockscontain 3 OFDM symbols, conforming to all the previous cases where 3OFDM symbols are needed for each VHT-SIG field. Also, in embodimentssimilar to those described above, the VHT-SIG placed after one VHT-LTFis applied regardless of DL-SDMA.

In the above mentioned examples in which two VHT-SIG blocks are present(e.g., one after L-SIG and the other after one of the VHT-LTFs), in someembodiments the two VHT-SIG blocks have different numbers of OFDMsymbols. For example, the first VHT-SIG block has 3 symbols and secondVHT-SIG block has 2 or 1 symbols. In another example, the first VHT-SIGblock has 2 symbols and the second VHT-SIG block has 1 symbol.

In some embodiments that support DL-SDMA, the same preamble utilizedregardless of DL-SDMA or not. In one embodiment of a non DL-SDMA case,the first VHT-SIG block signals the PHY information. In this embodiment,in the DL-SDMA case, the first VHT-SIG block delivers common PHYinformation for all the DL-SDMA users (e.g., bandwidth, short GI, etc.),and the second VHT-SIG block includes user-specific PHY information(e.g., MCS, length, etc.). In some embodiments, other fields are omittedin the second VHT-SIG block (e.g., sounding, extension, VHT-LTFs, etc.),so the second VHT-SIG block can be shorter than the first VHT-SIG block.

In one embodiment, the first VHT-SIG block has 2 OFDM symbols, and thesecond VHT-SIG block has 1 OFDM symbol, and the same preamble is appliedfor both single user and SDMA. In this embodiment, the first VHT-SIGalways signals common PHY information for all users regardless of singleuser or SDMA, and the second VHT-SIG block has user specific informationin the case of SDMA. For example, the first VHT-SIG block includesLength, GI Length, Bandwidth, Coding Type, Non-Sounding, number ofVHT-LTFs (or 1 bit for whether only single VHT-LTF is present for singleuser case), BCC Tail, CRC, according to an embodiment. On the otherhand, the second VHT-SIG block includes MCS, STBC type, smoothing, BCCTail, CRC, according to an embodiment. In other embodiment, some of theabove listed subfields are not present.

The IEEE 802.11n Standard specifies that, in mixed mode, the “Rate”subfield in L-SIG must be set to the lowest rate, i.e., 6 Mbps. Thefirst communication protocol, on the other hand, sets the “Rate”subfield in L-SIG to rate specified in the IEEE 802.11a Standard otherthan 6 Mbps, according to an embodiment. In this embodiment, an IEEE802.11n Standard compliant station, when decoding the L-SIG and findingRate is not 6 Mbps, will automatically treat the packet as a legacy IEEE802.11a packet, and set CCA according to the “Rate” and “Length”subfields in L-SIG. In an embodiment, one or more VHT-SIG symbols aremodified for detection according to the first communication protocol,such as described above (e.g., the various modulation techniquesdescribed above).

In embodiments similar to all of the above-described examples, thenumber of tones delivering VHT-SIG in each of the VHT-SIG OFDM symbolsis more than the number used in L-SIG. For example, 52 data tones areused in each of the VHT-SIG OFDM symbols, whereas 48 data tones are usedin L-SIG and HT-SIG (if utilized), in some embodiments. In anembodiment, the same tone mapping as in the IEEE 802.11n Standard for 20MHz and MCSO is utilized. In this embodiment, four more bits can bedelivered for VHT-SIG in each of the VHT-SIG OFDM symbols. In anembodiment, the long training field right before the VHT-SIG also sendsnon-zero training values (+−1) at these four additional tones.

FIG. 21A is a diagram of another example data unit 500, according to anembodiment, that can be used in both DL-SDMA and non DL-SDMA scenarios.A first portion of the data unit 470 includes L-STF, L-LTF, L-SIGfields, and VHT-SIGA fields 504. A second portion includes VHT-STF,VHT-LTF1, the zero or more VHT-LTF2 through VHT-LTFN fields 412, aVHT-SIGB field 508, and the VHT data portion 416. In the non DL-SDMAcase, the VHT data portion 416 includes data for a single device. In theDL-SDMA case, VHT-STF, VHT-LTF1, the VHT-LTF2 through VHT-LTFN fields412, the VHT-SIGB field 508, and the VHT data portion 416 includedifferent information for different client devices. In non-DL-SDMAcases, the first portion of the data unit 500 need not be steereddifferently than the second portion of the data unit 500 (e.g., need notbe unsteered vs. steered).

In an embodiment, the rate field in the L-SIG field is set to 6 Mbps,and the length field is set to indicate the duration T. In anembodiment, each VHT-SIGA field 504 includes two OFDM symbols: a firstsymbol and a second symbol. The VHT-SIGB field 508 has one OFDM symbol.FIG. 21B illustrates modulation applied to the L-SIG fields 112, thefirst symbols of the VHT-SIGA fields 504, and the second symbols of theVHT-SIGA fields 504.

The data unit 500 is an example data unit for an 80 MHz bandwidthtransmission. The data unit 500 can be suitably modified fortransmissions of different bandwidths as 20 MHz, 40 MHz, 160 MHz, etc.

In an embodiment, subfields of VHT-SIGA and VHT-SIGB are allocatedregardless of whether single user or multiple user (e.g., SDMA)transmission is being utilized. In this embodiment, VHT-SIG-A includestwo OFDM symbols VHT-SIG-B includes one OFDM symbol. In one example, 48tones are utilized in both VHT-SIG-A and VHT-SIG-B. In another example,52 tones are utilized in one or both of VHT-SIG-A and VHT-SIG-B.

In one specific embodiment, VHT-SIGA includes the following subfields:Length/Duration (16 bits) (can be defined in “number of OFDM symbols”,for example); Bandwidth (2 bits); Coding Type (1 bit); Not Sounding (1bit); Number of Extension VHT-LTFs (3 bits); Short GI (1 bit) (in oneimplementation, Short GI is not set to 1 in DL-SDMA if at least one useris utilizing a single stream, and at least one user is utilizing morethan one stream); Single VHT-LTF? (1 bit) (in one implementation, earlysignaling of short GI with a single stream (MCS is in VHT-SIG-B), and isnot set to 1 in downlink multi-user MIMO data units unless all users arewith single stream); CRC (8 bits); BCC tail bits (6 bits). In oneimplementation, the VHT-SIGA includes a “reserved” subfield.

In one specific embodiment, VHT-SIGB includes the following subfields:the MCS (8 bits); Aggregation (1 bit); STBC (2 bits); Smoothing (1 bit);CRC (4 bits); BCC tail bits (6 bits). In one embodiment, the smoothingsubfield is omitted. In one implementation, the VHT-SIGB includes a“reserved” subfield.

In one embodiment, the first symbol of VHT-SIGA is modulated using BPSK,whereas the second symbol of VHT-SIGA is modulated using Q-BPSK, asillustrated in FIG. 21B. In one embodiment, a faster clock as comparedto the IEEE 802.11n Standard is utilized for transmitting the preamble.In an embodiment, VHT-STF is longer as compared to HT-STF of the IEEE802.11n Standard, and/or longer the GI of VHT-LTF1 is longer as comparedto the GI of HT-LTF1 of the IEEE 802.11n Standard. This provides forbetter AGC performance especially at a transmit beamformee, in someimplementations. In one embodiment, a different modulation of the firstOFDM symbol of VHT-SIGA is utilized as compared to the IEEE 802.11nStandard, so the IEEE 802.11n Standard HT detection will still fail, buta client station configured according to the first communicationprotocol can determine that the data unit conforms to the firstcommunication protocol. For VHT-SIGA and/or VHT-SIGB, 48 or 52 tones areutilized, depending on the implementation, according to someembodiments.

In an embodiment, Q-BPSK is utilized on M_(Q) data tones in the firstsymbol of VHT-SIG-A or both of the symbols of VHT-SIG-A, and BPSK isutilized on the remaining M_(I)=48−M_(Q) data tones. As just twoexamples, the (M_(Q), M_(I)) tuple equals (24, 24) or (16, 32). In anembodiment, the different modulations are spread across the whole bandto explore frequency diversity, e.g. by equal or substantially equalseparations. The specific tone indices with the different modulationscan be specified by the first communication protocol.

In this embodiment, a client station configured according to the firstcommunication protocol can differentiate between first communicationprotocol data units, IEEE 802.11n Standard data units, and IEEE 802.11aStandard data units by comparing energy of Q-arm and I-arm across the 48tones. This is equivalent to delivering 2 information bits by the 48tones. A client station configured according to the IEEE 802.11nStandard, when receiving such a first communication protocol data unit,will fail detection of a HT IEEE 802.11n Standard data unit, and willthus treat the data unit as a IEEE 802.11a Standard data unit (i.e.,L-SIG spoofing).

In another embodiment, the legacy portion of a preamble utilizes the 4extra guard tones of the 20 MHz signal, which were allocated to the IEEE802.11n Standard 20 MHz data signal, but not to the IEEE 802.11a 20 MHzsignal. These 4 tones are not used to deliver data of VHT-SIG/L-SIGfields, but they are predefined to be non-zero symbols, e.g. in BPSK(+−1), or in Q-BPSK (+−j), in an embodiment. Whenever a firstcommunication protocol receiver detects that there are signals on these4 tones, and/or the detected symbols (after demodulation and slicing)matches the predefined symbols on these 4 tones, then the receiverdetermines that the data unit conforms to the first communicationprotocol.

In one embodiment, the data tones in the first OFDM symbol of VHT-SIG-Aare modulated using BPSK, so IEEE 802.11a/11n receivers will treat thedata unit as an 802.11a Standard data unit. In various embodiments, the4 extra tones are applied in L-SIG only, or both L-SIG and VHT-SIG-A, orfirst OFDM symbol of VHT-SIG-A only, or L-SIG and first OFDM symbol ofVHT-SIG-A, not in the remaining symbols of VHT-SIG, etc.

In these embodiments, the L-LTF also includes these 4 tones, which couldbe in the same way HT-GF-STF and GF-HT-LTF1 in green field mode of theIEEE 802.11n Standard 20 MHz signal. A receiver may detect the energy ofthese 4 tones across all the mentioned OFDM symbols (e.g. L-LTF, L-SIG,and 1st symbol of VHT-SIG-A), for detection of first communicationprotocol data units.

In embodiments in which VHT-SIG-B is placed after VHT-LTFn (e.g., afterthe last VHT-LTF, as in FIG. 21A), VHT-SIG-B is spatially mapped thesame way as VHT-LTFn (e.g. by vector QP_(n)) so a receiver can use thechannel estimation from VHT-LTFn to decode VHT-SIG-B. In anotherembodiment, VHT-SIG-B is spatially mapped the same way as VHT-LTF1 (e.g.by vector QP₁), so a receiver can use the channel estimation fromVHT-LTF1 to decode VHT-SIG-B.

In some embodiments VHT-SIG-B is placed after VHT-LTFn (e.g., the firstor the last VHT-LTF), no matter single user or multi-user packets. Inother embodiments, VHT-SIG-B is placed after VHT-LTF1 for single userand after VHT-LTFn for multi-user cases (e.g. after the first VHT-LTFfor single user, and after the last VHT-LTF for multi-user). In otherembodiments, VHT-SIGB does not exist for single user, and is applied formulti-user. In other embodiments, VHT-SIGB does not exist regardless ofsingle user or multi-user. In some embodiments, VHT-SIG-A includes a bitto indicate single user or multi-user, and a subfield to indicate atotal number of VHT-LTFs (which may be utilized by a receiver to locatethe position of VHT-SIG-B in embodiments and/or data units that includeVHT-SIG-B).

In one specific embodiment, VHT-SIGA includes the following subfields:Length/Duration (16 bits or some other suitable number) (can be definedin “number of OFDM symbols”, for example); Bandwidth (2 or more bits);Coding Type (1 bit); Not Sounding (1 bit); Smoothing (1 bit); Short GI(1 bit); CRC (8 bits); BCC tail bits (6 bits); a Number of ExtensionVHT-LTFs; Ness. In one implementation, the VHT-SIGA includes a“reserved” subfield.

In one specific embodiment, VHT-SIGB includes the following subfields:the MCS (any suitable number of bits); Aggregation (1 bit); STBC (anysuitable number of bits); CRC (any suitable number of bits, but can beless than 8 bits in one implementation); BCC tail bits (6 bits). In oneembodiment, the smoothing subfield is omitted from VHT-SIGA and includedin VHT-SIGB. In one embodiment, the aggregation subfield is omitted fromVHT-SIGB and included in VHT-SIGA. In one implementation, the VHT-SIGBincludes a “reserved” subfield.

If VHT-SIG-B is always placed after the last VHT-LTF regardless singleuser or multi-user transmission, a number of spatial stream (Nss) andSTBC can be signaled in VHT-SIG-A, according to an embodiment. In thisembodiment, in DL-SDMA case, Nss and STBC are constrained to be commonfor all the clients.

FIG. 22 is a diagram of another example data unit 550, according to anembodiment, that can be used in both DL-SDMA and non DL-SDMA scenarios.The data unit 550 is similar to the data unit 500 of FIG. 21A, but omitsthe VHT-SIGB field 508. The L-SIG fields 112 and the VHT-SIGA fields 504are modulated according to FIG. 21B, in an embodiment. The data unit 550is an example data unit for an 80 MHz bandwidth transmission. The dataunit 550 can be suitably modified for transmissions of differentbandwidths as 20 MHz, 40 MHz, 160 MHz, etc.

In some embodiments, the first communication protocol utilizesbeamforming and/or downlink multi-user multiple input, multiple output(DL-MU-MIMO). In these embodiments, the communication devices in anetwork utilize sounding data units (also referred to as soundingpackets) for beamforming and/or DL-MU-MIMO.

In some embodiments, a sounding data unit includes a preamble but omitsa data portion. In one embodiment of a sounding data unit, soundingsignals are included in the VHT-SIGB field. In other embodiments, thesounding data unit does not include the VHT-SIGB field.

In one embodiment, preambles of regular data units with data includeVHT-SIGB. In a particular embodiment, preambles of regular data unitswith data include VHT-SIGB, whereas sounding data units do not includeVHT-SIGB.

In one embodiment, the L-SIG field and/or the VHT-SIGA field and/or theVHT-SIGB field (if included) of a sounding data unit indicates that thedata unit does not have a data portion. In another embodiment, the L-SIGfield and/or the VHT-SIGA field and/or the VHT-SIGB field (if included)of a sounding data unit additionally or alternatively includes a“non-sounding” bit similar to the “non-sounding” bit in the HT-SIG fieldof the IEEE 802.11n Standard that indicates whether the data unit is asounding data unit.

In embodiments in which preambles of regular data units include VHT-SIGBwhereas the preambles of sounding data units do not include VHT-SIGB, areceiver determines whether VHT-SIGB is included in the preamble of areceived data unit based on the data length and/or “non-sounding”information from the L-SIG and/or VHT-SIGA fields.

FIG. 23 is a diagram of an example sounding data unit 600, according toan embodiment. The sounding data unit 600 omits a data portion. Thesounding data unit 600 includes an L-LTF field 604, an L-SIG field 608,a VHT-SIGA field having a first symbol 612 and a second symbol 616. Thesounding data unit 600 also includes a VHT-STF field 620, one or moreVHT-LTF fields 624, and a VHT-SIGB field 628. In one embodiment, theL-SIG field 604 and/or the VHT-SIGA field 612, 616 and/or the VHT-SIGBfield 628 indicates that the data unit does not have a data portion. Inanother embodiment, the L-SIG field 604 and/or the VHT-SIGA field 612,616 and/or the VHT-SIGB field 628 additionally or alternatively include“non-sounding” information (i.e., a “non-sounding” bit) that indicatesthat the data unit 600 is a sounding data unit.

FIG. 24 is a diagram of another example sounding data unit 650,according to an embodiment. The sounding data unit 650 is similar to thesounding data unit 600, but omits VHT-SIGB 628.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

1. A method for generating a data unit for transmission via acommunication channel, the data unit conforming to a first communicationprotocol, the method comprising: generating a preamble of the data unit,wherein the preamble includes a first field having information thatindicates a duration of the data unit, the first field being formattedsuch that the first field is decodable by a receiver device thatconforms to a second communication protocol but does not conform to thefirst communication protocol to determine the duration of the data unitbased on the first field, the preamble is formatted such that a portionof the preamble is decodable by a receiver device that conforms to athird communication protocol but does not conform to the firstcommunication protocol, and the preamble is formatted such that areceiver device that conforms to the first communication protocol candetermine that the data unit conforms to the first communicationprotocol; and generating a data portion of the data unit that conformsto the first communication protocol and does not conform to either (i)the second communication protocol or (ii) the third communicationprotocol.
 2. A method according to claim 1, wherein the portion of thepreamble that is decodable by the receiver device that conforms to thethird communication protocol but does not conform to the firstcommunication protocol includes the first field, and wherein the firstfield is formatted such that the first field is decodable by thereceiver device that conforms to the third communication protocol butdoes not conform to the first communication protocol to determine theduration of the data unit based on the first field.
 3. A methodaccording to claim 2, wherein the first field of the preamble includes arate subfield and a length subfield that indicate the duration of thedata unit.
 4. A method according to claim 1, wherein the first field ofthe preamble includes a subfield that is set to a value that contradictsthe second communication protocol.
 5. A method according to claim 4,wherein the value of the first subfield that contradicts the secondcommunication protocol indicates to the receiver device that conforms tothe first communication protocol that the data unit conforms to thefirst communication protocol.
 6. A method according to claim 1, whereina second field of the preamble includes a subfield that is set to avalue that contradicts the third communication protocol.
 7. A methodaccording to claim 6, wherein the subfield that is set to the value thatcontradicts the third communication protocol indicates to the receiverdevice that conforms to the third communication protocol to the waituntil the energy of the data unit drops out before switching to a clearchannel assessment (CCA) mode.
 8. A method according to claim 1, whereina second field of the preamble includes information that indicates theduration of the data unit, and wherein the portion of the preamble thatis decodable by the receiver device that conforms to the thirdcommunication protocol but does not conform to the first communicationprotocol includes the second field.
 9. A method according to claim 1,wherein a second field of the preamble is modulated using a modulationdifferent than specified by the third communication protocol.
 10. Amethod according to claim 9, wherein the modulation of the second fielddifferent than specified by the third communication protocol indicatesto the receiver device that conforms to the first communication protocolthat the data unit conforms to the first communication protocol.
 11. Amethod according to claim 10, wherein the modulation of the second fieldincludes binary phase shift keying (BPSK) modulation of a firstorthogonal frequency division multiplexing (OFDM) symbol, and whereinmodulation specified by the third communication protocol for a symbolcorresponding to the first OFDM symbol is BPSK modulation rotated by 90degrees (Q-BPSK).
 12. A method according to claim 10, wherein themodulation of the second field includes modulation of a second OFDMsymbol different than the modulation of the first OFDM symbol.
 13. Amethod according to claim 1, wherein the data portion includes data foronly a single receiver device.
 14. A method according to claim 1,wherein the data portion includes independent data for a plurality ofreceiver devices.
 15. A method according to claim 1, wherein the dataportion has a cumulative bandwidth greater than a bandwidth specified bythe second communication protocol and a maximum bandwidth specified bythe third communication protocol.
 16. A method according to claim 1,wherein the second communication protocol is the Institute forElectrical and Electronics Engineers (IEEE) 802.11a Standard.
 17. Amethod according to claim 16, wherein the third communication protocolis the IEEE 802.11n Standard.
 18. An apparatus, comprising: a wirelesslocal area network (WLAN) physical layer (PHY) unit configured to:generate a preamble of the data unit that conforms to a firstcommunication protocol, wherein the preamble includes a first fieldhaving information that indicates a duration of the data unit, the firstfield being formatted such that the first field is decodable by areceiver device that conforms to a second communication protocol butdoes not conform to the first communication protocol to determine theduration of the data unit based on the first field; the preamble isformatted such that a portion of the preamble is decodable by a receiverdevice that conforms to a third communication protocol but does notconform to the first communication protocol; the preamble is formattedsuch that a receiver device that conforms to the first communicationprotocol can determine that the data unit conforms to the firstcommunication protocol; and wherein the WLAN PHY unit is furtherconfigured to generate a data portion of the data unit that conforms tothe first communication protocol and does not conform to either (i) thesecond communication protocol or (ii) the third communication protocol.19. An apparatus according to claim 18, wherein the portion of thepreamble that is decodable by the receiver device that conforms to thethird communication protocol but does not conform to the firstcommunication protocol includes the first field, and wherein the firstfield is formatted such that the first field is decodable by thereceiver device that conforms to the third communication protocol butdoes not conform to the first communication protocol to determine theduration of the data unit based on the first field.
 20. An apparatusaccording to claim 18, wherein the first field of the preamble includesa rate subfield and a length subfield that indicate the duration of thedata unit.
 21. An apparatus according to claim 18, wherein the firstfield of the preamble includes a subfield that is set to a value thatcontradicts the second communication protocol.
 22. An apparatusaccording to claim 21, wherein the value of the first subfield thatcontradicts the second communication protocol indicates to the receiverdevice that conforms to the first communication protocol that the dataunit conforms to the first communication protocol.
 23. An apparatusaccording to claim 18, wherein a second field of the preamble includes asubfield that is set to a value that contradicts the third communicationprotocol.
 24. An apparatus according to claim 23, wherein the subfieldthat is set to the value that contradicts the third communicationprotocol indicates to the receiver device that conforms to the thirdcommunication protocol to the wait until the energy of the data unitdrops out before switching to a clear channel assessment (CCA) mode. 25.An apparatus according to claim 18, wherein a second field of thepreamble includes information that indicates the duration of the dataunit, and wherein the portion of the preamble that is decodable by thereceiver device that conforms to the third communication protocol butdoes not conform to the first communication protocol includes the secondfield.
 26. An apparatus according to claim 18, wherein a second field ofthe preamble is modulated using a modulation different than specified bythe third communication protocol.
 27. An apparatus according to claim26, wherein the modulation of the second field different than specifiedby the third communication protocol indicates to the receiver devicethat conforms to the first communication protocol that the data unitconforms to the first communication protocol.
 28. An apparatus accordingto claim 18, wherein the data portion has a cumulative bandwidth greaterthan a bandwidth specified by the second communication protocol and amaximum bandwidth specified by the third communication protocol.
 29. Amethod for generating a data unit for transmission via a communicationchannel, the data unit conforming to a first communication protocol, themethod comprising: generating a preamble of the data unit, wherein thepreamble is formatted such that a portion of the preamble is decodableby a receiver device that conforms to a second communication protocolbut does not conform to the first communication protocol to determinethat the data unit conforms to a third communication protocol, thepreamble is formatted such that a receiver device that conforms to thefirst communication protocol can determine that the data unit conformsto the first communication protocol; and generating a data portion ofthe data unit that conforms to the first communication protocol and doesnot conform to either (i) the second communication protocol or (ii) thethird communication protocol.
 30. A method according to claim 29,wherein a first field of the preamble substantially conforms to thethird communication protocol, and wherein the first field includes arate subfield and a length subfield that indicate the duration of thedata unit.
 31. A method according to claim 29, wherein a first field ofthe preamble substantially conforms to the third communication protocol,and wherein the first field of the preamble includes a subfield that isset to a value that contradicts the third communication protocol.
 32. Amethod according to claim 31, wherein the value of the first subfieldthat contradicts the third communication protocol indicates to thereceiver device that conforms to the first communication protocol thatthe data unit conforms to the first communication protocol.
 33. A methodaccording to claim 29, wherein a first field of the preamble ismodulated using a modulation different than specified by the secondcommunication protocol.
 34. A method according to claim 33, wherein themodulation of the second field different than specified by the secondcommunication protocol indicates to the receiver device that conforms tothe first communication protocol that the data unit conforms to thefirst communication protocol.
 35. An apparatus, comprising: a wirelesslocal area network (WLAN) physical layer (PHY) unit configured to:generate a preamble of the data unit that conforms to a firstcommunication protocol, wherein the preamble is formatted such that atleast a portion of the preamble is decodable by a receiver device thatconforms to a second communication protocol but does not conform to thefirst communication protocol to determine that the data unit conforms toa third communication protocol; the preamble is formatted such that areceiver device that conforms to the first communication protocol candetermine that the data unit conforms to the first communicationprotocol; and wherein the WLAN PHY unit is further configured togenerate a data portion of the data unit that conforms to the firstcommunication protocol and does not conform to either (i) the secondcommunication protocol or (ii) the third communication protocol.